Levitov, Leonid

Date: Friday, October 2, 2015
Time: 11:00
Place: ETH Zurich, Hönggerberg, HPF E 6
Host: Klaus Ensslin

Viscosity, Current Vortices and Negative Nonlocal Resistance in Graphene

Leonid Levitov
MIT, USA

Quantum-critical states of diverse strongly correlated systems are
predicted to feature universal collision-dominated transport resembling
that of viscous fluids. However, investigation of these phenomena has
been hampered by the lack of known macroscopic signatures of the
hydrodynamic regime at criticality. Here we identify vorticity as such a
signature and link it with an easily verifiable striking macroscopic
transport behavior. Produced by the viscous flow, vorticity can drive
electric current against an applied field, resulting in a negative nonlocal
voltage. We argue that the latter plays the same role for the viscous
regime as zero electrical resistance does for superconductivity. Besides
offering a diagnostic of viscous transport which distinguishes it from ohmic
currents, the sign-changing electrical response affords a robust tool for
directly measuring the viscosity-to-resistivity ratio. The strongly
interacting electron-hole plasma in high-mobility graphene provides a
bridge between quantum-criticality and the cornucopia of fluid mechanics
phenomena.